A computer network is a geographically distributed collection of interconnected communication links and segments for transporting data between nodes, such as computers. Many types of network segments are available, with the types ranging from local area networks (LAN) to wide area networks (WAN). For example, the LAN may typically connect personal computers and workstations over dedicated, private communications links, whereas the WAN may connect large numbers of nodes over long-distance communications links, such as common carrier telephone lines. The Internet is an example of a WAN that connects disparate networks throughout the world, providing global communication between nodes on various networks. The nodes typically communicate over the network by exchanging discrete frames or packets of data according to predefined protocols. In this context, a protocol consists of a set of rules defining how the nodes interact with each other.
Computer networks may be further interconnected by an intermediate network node, such as a router, having a plurality of ports that may be coupled to the networks. To interconnect dispersed computer networks and/or provide Internet connectivity, many organizations rely on the infrastructure and facilities of Internet Service Providers (ISPs). ISPs typically own one or more backbone networks that are configured to provide high-speed connection to the Internet. To interconnect private networks that are geographically diverse, an organization may subscribe to one or more ISPs and couple each of its private networks to the ISPs equipment. Here, the router may be utilized to interconnect a plurality of private networks or subscribers to an IP “backbone” network. Routers typically operate at the network layer of a communications protocol stack, such as the internetwork layer of the Transmission Control Protocol/Internet Protocol (TCP/IP) communications architecture.
Simple networks may be constructed using general-purpose routers interconnected by links owned or leased by ISPs. As networks become more complex with greater numbers of elements, additional structure may be required. In a complex network, structure can be imposed on routers by assigning specific jobs to particular routers. A common approach for ISP networks is to divide assignments among access routers and backbone routers. An access router provides individual subscribers access to the network by way of large numbers of relatively low-speed ports connected to the subscribers. Backbone routers, on the other hand, provide transports to Internet backbones and are configured to provide high forwarding rates on fast interfaces. ISPs may impose further physical structure on their networks by organizing them into points of presence (POP). An ISP network usually consists of a number of POPs, each of which comprises a physical location wherein a set of access and backbone routers is located.
As Internet traffic increases, the demand for access routers to handle increased density and backbone routers to handle greater throughput becomes more important. In this context, increased density denotes a greater number of subscriber ports that can be terminated on a single router. Such requirements can be met most efficiently with platforms designed for specific applications. An example of such a specifically designed platform is an aggregation router. The aggregation router, or “aggregator”, is an access router configured to provide high quality of service (QoS) and guaranteed bandwidth for both data and voice traffic destined for the Internet. The aggregator also provides a high degree of security for such traffic. These functions are considered “high-touch” features that necessitate substantial processing of the traffic by the router.
More notably, the aggregator is configured to accommodate increased density by aggregating a large number of leased lines from ISP subscribers onto a few trunk lines coupled to an Internet backbone. Increased density has a number of advantages for an ISP, including conservation of floor space, simplified network management and improved statistical performance of the network. Real estate (i.e., floor space) in a POP is typically expensive and costs associated with floor space may be lowered by reducing the number of racks needed to terminate a large number of subscriber connections. Network management may be simplified by deploying a smaller number of larger routers. Moreover, larger numbers of interfaces on the access router improve the statistical performance of a network. Packet networks are usually designed to take advantage of statistical multiplexing, capitalizing on the fact that not all links are busy all of the time. The use of larger numbers of interfaces reduces the chances that a “fluke” burst of traffic from many sources at once will cause temporary network congestion.
In addition to deployment at a POP, the aggregator may be deployed in a telephone company central office. The large numbers of subscribers connected to input interface ports of the aggregator are typically small to medium sized businesses that conduct a substantial portion of their operations “on-line”, e.g., over the Internet. Each of these subscribers may connect to the aggregator over a high reliability link connection that is typically leased from, e.g., a telephone company provider. The subscriber traffic received at the input interfaces is funneled onto at least one trunk interface. That is, the aggregator essentially functions as a large “fan-in” device wherein a plurality (e.g., thousands) of relatively low-speed subscriber input links is aggregated onto a single, high-speed output trunk to a backbone network of the Internet.
Redundancy techniques are used to protect against failures within an intermediate network node such as an aggregation router. Here, the failures may be directed to an input and/or output interface of the router or to the link connection (such as a fiber optic cable) coupled to the router. The interfaces may be embodied as multiple ports contained on a line card of the aggregator. In an implementation of multi-port line card redundancy, a plurality of external devices (such as end stations) is coupled to each line card via a link connection, such as a fiber cable.
Typically, if one of the redundant line cards fails (breaks), then a “switch over” operation is performed to allow the other line card to transmit and receive data to and from the end stations. Similarly, if a fiber cable connection coupling one of the line cards to an end station fails, thereby resulting in a failure of that line card, then the switch over operation allows the other line card to assume transmission and reception responsibility. However, a difficult situation is presented if one fiber cable coupling a first line card to a first end station fails, while substantially simultaneously a second fiber connection coupling a second line card of the redundant pair to a second end station fails. Here, the aggregation router cannot perform a switch over operation to switch from one line card to the other even though identical copies of data are presented from the end stations to each line card. This is because there are failures associated with different ports that are receiving different data from different end stations.
A conventional approach to this problem is to repair the failed fiber connection at one of the line cards to thereby enable that line card to assume transmission and reception responsibility for the router. However, many installations such as those at a telephone central office or a POP of an ISP have large amounts of cables (fiber or copper) connected to the line cards of the aggregator. These installations tend to “lash down” bundles of the cables to secure them in the event of a natural disaster such as, e.g., an earthquake. As a result, it is quite difficult to remove a fiber or copper cable connection that is tied down to various structures in such a natural disaster resistant manner. In the case of a fiber connection, the glass encompassing the fiber is quite fragile and prone to destruction in the event of excessive handling. This is a serious problem and the present invention is directed to providing a solution to this type of problem.
Another solution to the failed fiber connection problem involves disconnecting a functional fiber connection from one of the line cards and inserting it into the failed fiber connection of the other line card of the redundant pair, to thereby realize at least one complete functional line card. However, this approach requires human intervention in the sense that a technician must travel to the site and perform the swapping operation. Moreover, this approach is expensive in terms of time and resource consumption. The present invention is further directed to an efficient technique that enables automatic reconfiguration of a multi-port line card of an aggregation router in the event of a failure.